The invention relates to a method and apparatus for correcting the set value of the forging dimension in forging presses with forging tools constructed in V-shape, the forging press being controlled by means of distance-dependent operation of the valves, namely by the top or bottom reversal point being controlled during the forging operation after the comparison of set and measured values, the measured value being provided by a counter and by a transducer which is connected to the tup member, for example by means of a rack, and the set value for the forging dimension (per pass) is provided from the control console to the counter as a numerical value.
It is known that when forging with flat dies the forming surfaces of the top and bottom die are parallel to each other in the horizontal plane. The position when the forming surfaces of the top and bottom die bear on each other is regarded as the reference point or reference plane (zero point) for setting the forging dimension.
The distance between the above-mentioned surfaces in the operating state is measured by means of a digital transducer which is set into rotary motion, for example by a rack that is connected to the tup member, thus producing an electrical distance simulation of the operating stroke in an electric pulse sequence. The measured dimension of the stroke represents the distance between the forming surfaces of the top and bottom die at the end of the stroke and also defines the dimension, after forging, of the workpiece. During forging, the forging dimension is compared by suitable electrical means with a predefined set value. The relative motion between top and bottom die is, at least theoretically, completed when the set value and the measured forging dimension correspond to each other.
Forging with so-called V-dies instead of forging with flat dies has been common practice for several decades. In this kind of forging each of the top and bottom dies is provided with a V-shaped recess to receive the material for forging. The V-shaped recesses are constructed symmetrically to the horizontal plane. When V-dies, with a vertex angle of 90.degree., meet each other, a square opening will be formed the diagonals of which run vertically and horizontally. The width across flats, i.e. the distance between the two parallel oppositely disposed die surfaces will be represented by d. When the V-dies meet, the width across flats of the square opening will be d.sub.min. The V-dies can also have vertex angles other than 90.degree., e.g. 45.degree. or less.
One pair of V-dies permits forging of workpieces which have diameters ranging from d.sub.min to 2 .times. d.sub.min. This applies to all rectangular, polygonal or round workpieces.
Forging rectangular, polygonal or round sections with V-dies gives rise to the problem that the distance between the forming surfaces (the Veed surfaces) of the bottom and top die does not usually coincide with the forging dimension of the workpiece disposed between the surfaces, because the distance between the forming surfaces is at an angle to the vertical direction of motion of the forging dies. It is not therefore practical to use the distance between the forming surfaces of the top and bottom die either for measuring the forging dimension, or for comparison with a set value as a reference point for the forging dimension.
Instead, based on experience and measurement of the diameter of the workpiece after each manual forging pass, it has become acceptable practice to gradually approach the desired finishing dimension of the workpiece by manually setting the forging dimension.
Such manual operation of the forging press requires, for obvious reasons, a substantial amount of time and results in throughput losses because the available press force of the forging press cannot be fully utilized during the last passes if rejects due to undersized dimensions are to be avoided.